I want to find differential expressed genes between two RNASeq samples in Galaxy.

I want to use CuffMerge to merge assembled transcripts produced by Cufflinks.

In the first box the list of all Cufflinks output is shown(when I choose multiple datasets), but when I choose the option to import additional gtf file , it is empty and says me there is nothing to show.

Dataset collections versus individual datasets labeled with the metadata "dataytpe" assignment of GTF are accepted by these input fields.

If you are working on another server, then contacting the administrators is the best path forward. This list of known Public Galaxy servers (should you be working at one of these) often has contact info - or look for it on the server's home page: https://wiki.galaxyproject.org/PublicGalaxyServers